This invention relates to blind fasteners and more particularly to blind fasteners having a large bearing surface on the blind side of the structure on which it is mounted.
As discussed in the co-pending patent application by Cu Soc Huynh and John D. Pratt entitled "COMPOSITE BLIND FASTENER" Ser. No. 229,323 filed Jan. 29, 1981 and assigned to the same assignee as this patent application, three piece blind fasteners have been known and used for many years wherein the three pieces consist of a nut threaded onto a bolt and an expansible sleeve is located therebetween. As discussed in said co-pending patent application, prior three piece blind fasteners were found to encounter significant problems when utilized with sheets of material which are relatively soft or material such as a graphite composite or when utilized in structures in which very thin sheets of material are utilized on the blind side because the force applied by the sleeve on the blind side surface would be sufficiently high to deform the blind side surface and weaken the sheet at that point. Consequently the patents described in said co-pending patent application and the invention described in said co-pending patent application were developed to achieve a large bearing surface on the blind side so that such materials could be properly fastened with minimal damage to the blind side. However, each of such aforementioned prior inventions has a number of disadvantages associated therewith which the present invention overcomes. For example, the fastener of U.S. Pat. No. 4,203,346 to Hall et al. and in the aforementioned co-pending patent application produce a relatively small bearing surface on the blind side particularly compared to the length of sleeve employed. Further the fact that Hall et al. rely upon the shoulder 27 of the nut 10 to bend the sleeve radially outward against the back surface creates a tendancy to delaminate the back surface adjoining the nut 10 at shoulder 27. Moreover, the internal taper of the sleeve bore in Hall et al. increases its cost to manufacture. On the other hand the fastener described in Wilson U.S. Pat. No. 4,033,222 has different disadvantages because due to its design it has relatively high blind side protrusion which limits its use to areas with sufficient clearance on the blind side. Further, because of its number of parts it is relatively heavier and more expensive than the simple three piece blind fastener.
In response to such disadvantages, an object of the present invention is a blind fastener which can achieve a large bearing surface on the blind side with an installed collar although the collar described below can be a separate piece if desired.
Another object of the present invention is a blind fastener which achieves such large bearing area with a single folded sleeve and without relying on a nut shoulder to apply the compressive supporting force on the sleeve.
Still another object of the present invention is a blind fastener which has low blind side protrusion, light weight and low cost but still provides a large uniform bearing surface on the blind side.
Still another object of the present invention is a blind fastener with a sleeve adapted to buckle to permit flush breakoff of the fastener bolt stem throughout the fastener grip range.
Other objects and advantages of the present invention will be readily apparent from the following description and drawings which illustrate a preferred exemplary embodiment of the present invention.